Electrolytic hydrodimerization of 2-or 4-alk-1-enyl pyridines, e. g., vinyl pyridines



United States Patent 3 218,246 ELECTROLYTIC HiKDRODIMERIZATION 0F 2- 0R4-ALK-1-ENYL PYRIDINES, e.g., VINYL PYRIDINES Manuel M. Baizer andErhard J. Prill, St. Louis, Mo., assignors to Monsanto Company, acorporation of Delaware No Drawing. Filed June 18, 1963, Ser. No.288,621 Claims. (Cl. 204-74) The present invention relates to themanufacture of poly-functional compounds and more particularly providesa process for electrolytically hydrodimerizing compounds havingethylenic bonds in conjugated relationship to the unsaturated system ofa pyridine ring.

An object of the invention is the provision of a process for preparingbutanes bearing 2- or 4-pyridine substituents in the 1 and 4 positions,e.g., l,4-bis(2-pyridyl) butane.

The process of tthe present invention is illustrated:

in which Z is a pyridine radical attached at the 2 or 4 position, i.e.,an even numbered ring carbon atom, and R and R are hydrogen orhydrocarbyl radicals usually containing no non-benzenoid unsaturation,e.g., alkyl or aryl radicals. The pyridyl radicals can optionally besubstituted by alkyl radicals, particularly lower alkyl radicals, suchas methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, pentyl, hexyl,isohexyl, etc., groups, e.g., such 2- and 4-pyridyl radicals asZ-pyridyl, 4pyridyl, 3-methyl- Z-pyridyl, 3,'6-dimethyl-'2-pyridyl,2-methyl-4-pyridyl, 4- hexyl-Q-pyridyl, etc., are suitable, and thepyridyl radicals can also contain other nonreactive substituents whichdo not undergo undesired transformations during the electrolysisprocedure. It is necessary to have the pyridyl group bonded to theethylene at the 2 or 4 position in order to have the ethylenic bondproperly activated for the electrolysis. The position on the pyridinering in the product will correspond to that in the reactant. The R and Rsubstituents are individually selected from hydrogen, alkyl or arylgroups, e.g., hydrogen, methyl, ethyl, propyl, isopropyl, butyl, hexyl,phenyl, alpha-naphthyl, beta-naphthyl, 2-ethylpheny1, benzyl,phenylethyl, etc. Some examples of suitable reactants areZ-Vinylpyridine, 4-vinylpyridine, 2-crotylpyridine,4-but-1-enylpyridine, 2- hex-l-enyl-4-rnethylpyridine,2(2-pyridyl)propene, 2- styrylpyridine, 1(2-pyridyl)-2-(2-tolyl-etheneand various other '2 or 4 pyridyl ethylenes. While in general thealpha,beta-olefinic substituents on the pyridine ring are hydrocarbyl,i.e., l-alkenyl groups, it is contemplated that the ethylenic carbonatoms can bear other functional groups which activate the olefinic bond,e.g., carbalkoxy, carboxamido or cyano groups. However, the presentinvention is concerned with the electrolytic reductive coupling of 2 or4-olefinic pyridines, not with coupling such pyridines with otheractivated olefinic compounds as disclosed and claimed in thesimultaneously filed copending application S.N. 288,629.

In .general, the electrolytic reductive coupling of the presentinvention is conducted in concentrated solution in an aqueouselectrolyte. It is desirable to employ fairly concentrated solutions inorder to minimize undesired reactions of intermediate ions with theWater of the electrolyte. The olefinic reactants will ordinarilycomprise at least about 10% by weight of the electrolyte, and preferablyat least by weight or more. It is generally desirable to employ fairlyhigh concentrations of salts in the electrolyte, for exampleconstituting 5% and usually 30% or more by weight of the total amount of3,218,246 Patented Nov. 16, 1965 salt and water in the electrolyte, inorder to obtain the desired solubility of the olefinic compounds.

Electrolysis, of course, has been practiced for many years and numerousmaterials suitable as electrolytes are known, making it within the skillof those in the art in the light of the present disclosure to selectelectrolytes for reductive coupling according to the present invention.Some olefinic compounds are subject to polymerization or other sidereactions if the electrolyte is acidic, or excessively alkaline, and itwill be necessary in such cases to conduct the reductive coupling insolutions which are not overly acidic and also in some cases below a pHat which undesirable side reactions occur, e.g., below about 12. Ingeneral, the 2- or 4-olefinic pyridine compounds employed in the presentinvention can be polymerized, and the pH is usually maintained withinthe range of about 3 to about 12 to obtain desired yields, preferablypHs of 6 to 9.5.

When the catholyte during electrolysis is acidic, it will generally beadvisable to conduct the electrolysis under conditions which inhibitpolymerization of the reactants involved or in the presence of apolymerization inhibitor for example, in an atmosphere containingsuflicient oxygen to inhibit the polymerization in question, or in thepresence of inhibitors effective for inhibiting free radicalpolymerization. Classes of inhibitors for inhibiting free radicalpolymerizations are well known, e.g., such inhibitors as hydroquinone,p-t-butyl catechol, quinone, p nitroso dimethylaniline, di-t-butylhydroquinone, 2,5-dihydroxy-1,4-benzoquinone, 1,4-naphthoquinone,chloranil, 9,10-phenanthraquinone, 4-amino-1-naphthol, etc., aresuitable.

In elfecting the reductive coupling of the present invention it ispreferred to utilize a cathode having an overvoltage greater than thatof copper and to subject to electrolysis in contact with such cathode aconcentrated solution of the defined olefinic compounds in an aqueouselectrolyte under mildly alkaline conditions. It is understood that boththe cathode and the anode will be in actual direct physical contact withelectrolyte. In effecting the reductive couplings of the presentinvention, it is essential to obtain cathode potentials required forsuch couplings and therefore the salt employed should not containcations which are discharged at numerically substantially lower, i.e.,less negative, cathode potentials. It is desirable that the saltemployed have a high degree of water solubility to permit us of veryconcentrated solutions, for concentrated salt solutions dissolve greateramounts of the organic olefinic compounds.

In addition to the foregoing considerations, a number of other factorsare important in selecting salts suitable for good results. For example,it is undesirable that the salt cation form an insoluble hydroxide atthe operating pH, or that it discharge on the cathode forming an alloywhich substantially changes the hydrogen overvoltage and leads to poorercurrent efficiencies. The salt anion should not be lost by discharge atthe anode with possible formation of by-products. If a cell containing aseparating membrane is used, it is desirable to avoid types of anionswhich, in contact with hydrogen ions present in the anolyte chamber,would form insoluble acids and clog the pores of the membrane.Alternatively, the use of an ion exchange membrane eifectively separatescatholyte and anolyte and the use of different anions in the twochambers may minimize any difficulties a particular anion would cause inone of the chambers.

In general amine and quaternary ammonium salts are suitable for use inthe present process. Certain salts of alkali and alkaline earth metalscan also be employed to some extent, although they are more subject tointerfering discharge at the cathode and the alkaline earth metal saltsin general tend to have poor water solubility, making their useinadvisable.

Example 1 A catholyte was prepared by mixing 43 grams of 85% by weightmethyl triethylammonium p-toluenesulfonate in water and 43 grams4-vinylpyridine to form a solution and diluting with 43 gramsdimethylformamide to a convenient volume. A small amount of hydroquinonewas added as stabilizer. The cathode was 110 ml. mercury. As anolyte, 15ml. of the 85 salt solution was diluted with 5 ml. water and placed inan Alundum cup in which a platinum anode was immersed. Electrolysis wasconducted for about two hours at cell voltage of about 30, cathodevoltage of l.4 to 1.5 (vs. saturated calomel electrode) and a current ofabout 2 amperes for a total of 3.8 ampere hours. During the electroylsisabout 3.7 ml. acetic acid was added to the catholyte to control thealkalinity. The solid l,4-bis(4-pyridyl)butane product, 6 grams, wasseparated by filtration, using dimethylformamide for washing, and driedto a white solid, M.P. 120 C. By diluting the filtrate with water,extracting with methylene dichloride, absorbing on and eluting from analumina column, an additional 6.4 grams of product, M.P. 119-121, wasisolated, for a yield of 82%.

Example 2 employing a solution of 50 grams 85% by weight methyltriethylammonium methylsulfate in water, 50 grams dimethylformamide and50 grams 2-vinylpyridine as catholyte. The anolyte was a 47% aqueoussolution of methyl tributylammonium p-toluenesulfonate. The electrolysiswas conducted at 1.4 to 1.5 cathode volts (vs. saturated calomelelectrode) for a total of 5.4 ampere hours. The catholyte was dilutedwith water and extracted with methylene dichloride, dried over calciumsulfate, and distilled under vacuum, using hydroquinone as stabilizer.About 30 grams of vinyl pyridine was recovered, and grams product wasobtained. The product was redistilled through micro apparatus, fractionsbeing collected at 124-6" at 0.2 mm. and 128 at 0.2 mm. The samplesanalyzed as 1, 4-bis(2-pyridyl)butane. Calcd: C, 79.2; H, 7.6; N, 13.2;Mol. wt. 212. Found: C, 77.22 .and 78.47; H,7.85 and 7.86; N, 12.35 and12.47; Mol. wt. 215 and 213. The infra red spectra of the sample wereidentical and confirmed the 1,4-bis(2-pyridyl) butane structure.

The above examples are illustrative of the present process and thereductive couplings of the various olefinic pyridines set forth hereincan be conducted under the same conditions or numerous variationsthereof. In addition, the procedures of copending application S.N.228,740, filed October 5, 1962, and now abandoned, and of theapplication referred-to therein are applicable to the hydrodimerizationof the olefinic pyridine reactants employed herein.

While high concentrations of the reactants are readily obtained withsome salts, concentrations can be increased by using a polar solventalong with the water, e.g., acetonitrile, dioxane, ethylene glycol,dimethylformamide, dimethylacetamide, ethanol or isopropanol, inaddition to the salts.

The electrolytic reductive couplings of the present invention areconducted in solution in electrolyte, generally in fairly concentratedsolution in an aqueous electrolyte. It will be recognized that as usedherein an electrolyte is considered aqueous even if the amount of wateris small. Many electrolytes can be employed in the present invention butsome are less suitable than others. The salts employed, either toprovide conductivity or to increase solubility of the reactants have animportant hearing on the electrolysis and will be discussed at lengthbelow. The acidity or basicity is also significant, neutral or mildyalkaline solutions generally being preferred.

Many of the olefinic compounds employed in the present invention tend topolymerize when electrolyzed in strongly acidic solution, such assolutions of mineral acids, and it is desirable or necessary in suchcases to avoid excesive acidity, making it desirable to operate at pHsabove about 5 or 6, such as provided by solutions of salts of strongbases. Moreover, the hydrogen ion has a cathode discharge potential ofabout 1.5 volts, making it desirable to avoid high concentrations ofhydrogen ion in the catholyte if the reductive coupling occurs atsimilar or more negative cathode potentials. The reductive couplings cansuitably be conducted at pHs higher than those at which substantialpolymerization of olefinic compound occurs, or higher than those atwhich there is undue generation of hydrogen, for example pHs at whichmore than half the current is expended in discharging hydrogen ions. ThepHs referred to are those obtaining in the buk of the catholytesolution, such as determinable by a pH meter on a sample of thecatholyte removed from the cell. The electrolysis in effect generatesacid at the anode and base at the cathode; it will be recognized that inan undivided cell the pH in the immediate vicinity of the cathode maydiifer considerably from that near the anode, particularly if goodstirring is not employed. To some extent the effects of acidity can becounteracted by high current density to cause more rapid generation ofhydroxyl ions. However, high current densities also require goodstirring or turbulence to move the reactants to the cathode.

During the electrolysis in a divided cell, alkalinity increases in thecatholyte. However, the anolyte becomes acidic. When a porous diaphragmis used to separate the catholyte from the anolyte, the alkalinity ofthe catholyte will depend upon the rate of difiusion of acid from theanolyte through the porous barrier. Control of alkalinity in thecathoylte when employing a diaghragm, may thus be realized by purposelyleaking acid from the anolyte into the catholyte. It can also beachieved, of course, by extraneous addition to the catholyte of an acidmaterial, e.g., glacial acetic acid, phosphoric acid orp-toluenesulfonic acid. Alkalinity may also be controlled, whether ornot a diaphragm is used inthe cell, by employing buffer systems ofcations which will maintain the pH range while not reacting at thereaction conditions.

It is known that strongly alkaline solution can cause pyridethylationreactions of vinyl pyridines and it will be desirable to maintain the pHlow enough to avoid or substantially minimize such reactions, forexample below 9.5. However, good agitation or turbulence may counteractexcess alkalinity to some extent by minimizing local concentrations ofhydroxyl ions at the cathode. The use of high current densities andother provisions to minimize the electrolysis reaction time will also beuseful in this regard.

When a divided cell is employed, it will often be desirable to use anacid as the anolyte, any acid being suitable, particularly dilutemineral acids such as sulfuric or phosphoric aid. Hydrochloric acid canbe employed but would have the disadvantage of generating chlorine atthe anode, and of being more corrosive with respect to some anodematerials. When an acid is employed as anolyte, it is advantageous touse an ion exchange membrane to separate the anolyte from the catholyte.If desired, a salt solution can be used as anolyte, those useful ascatholyte also being suitable as anolyte, although there are many othersalt solutions suitable for such use.

Material-s suitable for constructing the electrolysis cell employed inthe present process are well known to those skilled .in the art. Theelectrodes can be of any suitable cathode and anode material. The anodemay be of virtually any conductor, although it will usually beadvantageous to employ those that are relatively inert or attacked orcorroded only slowly by the electrolytes; suitable anodes are, forexample, platinum, carbon, gold, nickel, nickel silicide, Duriron, lead,and lead-antimony and leadcopper alloys, and alloys of various of theforegoing and other metals.

Any suitable material can be employed as cathode, various metals andalloys being known to the art. It is generally advantageous to employmetals of fairly high hydrogen overvoltage in order to promote currentefficiency and minimize generation of hydrogen during the electrolysis.In general it will be desirable to employ cathodes having overvoltagesat least about as great as that of copper, as determined in a 2Nsulfuric acid solution at current density of 1 miliarnp/squarecentimeter (Carman, Chemical Constitution and Properties of EngineeringMaterials, Edward Arnold and Co., London, 1949, page 290). Suitableelectrode materials include, for example, mercury, cadmium, tin, zinc,bismuth, lead, graphite, aluminum, nickel, etc., in general those ofhigher overvoltage being preferred. It will be realized that overvoltagecan vary with the type of surface and prior history of the metal as wellas with other factors; therefore the term overvoltage as used hereinwith respect to copper as a gauge has reference to the overvoltage underthe conditions of use in electrolysis.

Among the salts which can be employed according to the present inventionfor obtaining the desired concentration of dissolved olefinic compound,the amine and quaternary ammonium salts are gene-rally suitable,especially those of sulfonic and alkyl sulfuric acids.

Such salts can be the saturated aliphatic amine salts or heterocyclicamine salts, e.g., the mono-, dior tri-alkylamine salts, or the mono-,dior trialkanolamine salts, or the piperidine, pyrrolidine or morpholinesalts, e.g., the ethylamine, dimethylamine or triisopropylamine salts ofvarious acids, especially various sulfonic acids. Especially preferredare aliphatic and heterocyclic quaternary ammonium salts, i.e., thetetraalkylammonium or the tetraalkanolammonium salts or mixed alkylalkanol ammonium salts such as the alkyltrialkanolammonium, thedialkyldialkanolammonium, the alkanoltrialkylammonium or theN-heterocyclic N-alkyl ammonium salts of sulfonic or other suitableacids. The saturated aliphatic or heterocyclic quaternary ammoniumcations in general have suitably high cathode discharge potentials foruse in the present invention and readily form salts having suitably highwater solubility with anions suitable for use in the electrolytesemployed in the present invention. The saturated, aliphatic orheterocyclic quaternary ammonium salts are therefore in general welladapted to dissolving high amounts of olefinic compounds in theiraqueous solutions and to effecting reductive couplings of such olefiniccompounds. It is understood, of course, that it is undesirable that theammonium groups contain any reactive groups which might interfere tosome extent with the reductive coupling reaction. In this connection itshould be noted that aromatic unsaturation as such does not interfere asbenzyl substituted ammonium cations can be employed; (as also can arylsulfonate anions).

Among the anions useful in the electrolytes, the aryl and alkarylsulfinic acids are especially suitable, for example, salts of thefollowing acids; benzenesulfonic acid, 0-, mor p-toluenesulfonic acid,0-, mor p-ethylbenzenesulfonic acid, o-, mor p-cumenesulfonic acid, o-,mor -p-tert-a myl-benzenesulfonic acid, 0-, mor p-hexylbenzensulfonicacid, o-xylene-4-sulfonic acid, p-xylene-2- sulfonic acid, m-xylene-4 orS-sulfonic acid, mesitylene- 2-sulfonic acid, durene-3-sulfonic acid,pentamethylbenenesulfonic acid, o-dipropylbenzene-4-sulfonic acid,alphaor beta-naphthalenesulfonic acid, o-, mor p-biphenylsulfonic acid,and alpha-methylbet-a-naphthalenesulfonic acid. Alkali metal salts areuseful in the present invention with certain limitations, and the alkalimetal salts of such sulfonic acids can be employed, i.e., the sodium,potassium, lithium, cesium or rubidium salts such as sodiumbenzenesulfon-ate, potassium, p-toluenesulfonate, lithiumo-biphenylsulfonate, rubidium betanaphthalenesulfonate, cesiump-ethylbenzenesulfonate,

sodium o-xylene-Seulfonate, or potassium pentamethylbenzenesulfonate.also be the saturated, aliphatic amine or heterocyclic amine salts,e.g., the mono-, dior trialkylamine salts, or the mono-, diortrialkanolamiue salts, or the piperidine, pyrrolidine or morpholinesalts, e.g., the ethylamine, dimethylamine or triisopropylamine salt ofbenzenesulfonic acid or of o-, por m-toluenesulfonic acid; theisopropanolamine, dibutanolamine or triethanolarnine salt of o-, porm-toluenesulfonic acid or of o-, por m-biphenylsulfonic acid; thepiperidine salt of alphaor betanaphthalenesulfonic acid or of thecumenesulfonic acids; the pyrrolidine salt of o-, m-,p-amylbenzenesulfonate; the morpholine salt of henezesulfonic acid, ofo-, mor p-toluenesulfonic acid, or of .alphaor beta-naphthalenesulfonicacid, etc. In general, the sulfonates of any of the ammonium cationsdisclosed generically or specifically herein can be employed in thepresent invention. The aliphatic sulfonates are prepared by reaction ofthe correspondingly substituted ammonium hydroxide with the sulfonicacid or with an acyl halide thereof. For example, by reaction of asulfonic acid such as p-toluenesulfonic acid with a tetraalkylammoniumhydroxide such as tetraethyla'mmonium hydroxide there is obtainedtetraethylammonium p-toluenesulfonate, use of which in the presentlyprovided process has been found to give very good results. Otherpresently useful quaternary ammonium sulfonates are, e.g.,tetraethylammonium oor mtoluenesulfonate or benzenesulfonate;tetraethylammonium o-, mor p-cumenesulfonate or o-, morp-ethylbenzenesulfonate, tetramethylammonium benzenesulfonate, or 0-,mor p-toluenesulfonate; N,N-di-methylpiperidiniu-m o-, morp-toluenesulfonate or o-, mor p-biphenylsulfonate; tetrabutylammoniumalphaor betanaphthalenesulfonate or o-, mor p-toluenesulfonate;tetrapropylammonium o-, mor p-arnylbenezenesulfonate oralpha-ethyl-beta-naphthalenesulfonate; tetraethanolammonium o-, morp-cumene sulfonate or o-, mor p-toluenesulfonate; tetra-butanola-mmoniumbenzenesulfonate or p-xylene-3-sulfonate; tetrapentylammonium o-, morp-toluenesulfonate or o-, mor p-hexylbenzenesulfonate,tetrapentanolammonium p-cumene-3- sulfonate or benzenesulfonate;methyltriethylammonium o-, mor p-toluenesulfonate ormesitylene-Z-sulfonate; trimethylethylarnmonium o-xylene-4-sulfonate oro-, rnor p-toluenesulfonate; triethylpentylammonium alphaorbeta-naphthalene sulfonate or o-, mor p-butylbenzenesulfonate,trimethylethanolammonium benzenesulfonate or o-, mor p-toluenesulfonate;N,N-di-ethylpiperidinium or N-methyl-pyrrolidinium o-, morp-hexyl-benzenesulfonate or o-, m, or p-toluenesulfonate,N,N-di-isopropyl or N,N-di-butylmorpholinium o-, mor p-toluenesulfonateor o-, mor p-biphenylsulfonate, etc.

The tetraalkylammonium salts of the aryl or alkarylsulfonic acids aregenerally preferred for use as the salt constituents of the electrolysissolution because the electrolyses in the tetraalkylammonium sulfonatesare exclusively electrochemical processes.

Among the ammonium and amine sulfonates useful as electrolytes in thepresent invention are the alkyl, aralkyl, and heterocyclic amine andammonium sulfonates, in which ordinarily the individual substituents onthe nitrogen atom contain no more than 10 atoms, and usually the amineor ammonium radical contains from 3 to 20 carbon atoms. It will beunderstood, of course, that diand poly-amines and diand poly-ammoniumradicals are operable and included by the terms amine and ammonium. Thesulfonate radical can be from aryl, alkyl, alkaryl or aralkyl sulfonicacids of various molecular Weights up to for example 20 carbon atoms,preferably about 6 to 20 carbon atoms, and can include one, two or moresulfonate groups. Any of the quaternary ammonium sulfates disclosed andclaimed in copending application SN. 75,- 123 filed December 12, 1960can suitably be employed.

Another especially suitable class of salts for use in the The salts ofsuch sulfonic acids may present invention are the alkylsulfate saltssuch as methosulfate salts, particularly the amine and quaternaryammonium methosulfate salts. Methosulfate salts such as themethyltriethylammonium, tri-n-propylmethylammoniurn,triamylmethylammonium, tri-n-butylmethylammonium, etc., are veryhygroscopic, and the tri-n-butylmethylammonium in particular forms veryconcentrated aqueous solutions which dissolve large amounts of organicmaterials. In general the amine and ammonium cations suitable for use inthe alkylsulfate salts are the same as those for the sulfonates.

The 1,4-bis(pyridyl)butanes produced by the present invention are aknown class of compounds and the diquaternary salts formed therefrom byreaction with alkyl halides are known to have germicidal activity and toalso have curare-like activity and neuromuscular blocking activity whenhydrogenated to the corresponding alkylpiperidinium salts.

What is claimed is:

1. The method of reductively coupling pyridyl ethylenes which comprisessubjecting a solution of such compound to electrolysis in contact with acathode, the said pyridyl ethylenes having the pyridyl ring bonded tothe ethylene by one of the even-numbered ring carbon atoms with respectto the nitrogen atom.

2. The method of claim 1 in which a 2-vinyl pyridine is hydrodimerizedto a 1,4-bis(2-pyridyl)butane.

3. The method of claim 1 in which a 4-vinyl pyridine is hydrodimerizedto a l,4-bis(4-pyridyl)butane.

4. The method of hydrodimerization which comprises subjecting an aqueoussolution of olefinic compound represented by the formula:

in which Z represents a pyridyl radical with its valence bond on aneven-numbered carbon atom, and R and R are selected from the groupconsisting of hydrogen and hydrocarbyl radicals containing nonon-benzenoid unsaturation to electrolysis in contact with a cathodehaving a hydrogen overvoltage greater than that of copper, causingdevelopment of the cathode potential required for bydrodimerization, thesolution containing at least about 10% by weight of olefinic compoundand having a pH above about 6, and recovering the resulting bis pyridylbutane.

I 5. The method of claim 4 in which the olefinic compound is a 2-vinylpyridine.

6. The method of claim 4 in which the olefinic compound is 4-vinylpyridine.

7. The method of claim 4 in which the pH is about 7 to 9.5.

8. The method of claim 1 in which a polymerization inhibitor is present.

9. The method of claim 4 in which an aqueous electrolysis solution isemployed and a quaternary ammonium salt constitutes at least 30% byweight of the water and salt, the said salt being soluble in suchamounts.

10. The method of claim 1 in which the electrolysis is conducted in aquaternary ammonium aromatic sulfonate solution.

References Cited by the Examiner UNITED STATES PATENTS 2,632,729 3/1953Woodman 20472 2,726,204 12/ 1955 Park et a1. 20472 OTHER REFERENCESTechnique of Organic Chemistry, vol. II, Catalytic, Photochemical,Electrolytic Reactions, 2nd edition, 1956, Interscience Publishers,Inc., New York, pages 435 and 451- 457.

JOHN H. MACK, Primary Examiner.

1. THE METHOD OF REDUCTIVELY COUPLING PYRIDYL ETHYLENES WHICH COMPRISESSUBJECTING A SOLUTION OF SUCH COMPOUND TO ELECTROLYSIS IN CONTACT WITH ACATHODE, THE SAID PYRIDYL EHTYLENES HAVING THE PYRIDYL RING BONDED TOTHE ETHYLENE BY ONE OF THE EVEN-NUMBERED RNG CARBON ATOMS WITH RESPECTTO THE NITROGEN ATOM.